The present invention relates to techniques for optically reproducing information.
FIG. 2 shows one exemplary configuration of a magneto-optical recording/reproduction device which is one of prior known optical record/playback devices. Laser light emitted from a laser 311 mounted on an optical head 3 is collimated by a collimator lens 312 into parallel rays of light, which are guided via a beam splitter 324 to a lens 321 that forms a light spot 21 on a magnetooptical recording medium 8. The position of the light spot 21 on the magnetooptical recording medium 8 is controllable by movement of the lens 321 and optical head 3 under control of an optical spot scan control means 63. Reflection light from the magnetooptical recording medium 8 is guided by the beam splitter 324 toward a photodetector means 33. A reproduction signal from the photodetector 33 is processed by a reproduction circuit 93 for conversion to reproduction data. These overall reproduction operations are under control of a controller 55.
As a method for reproducing information as recorded in high density using the optical record/reproduction device, a magnetic super-resolution reproduction method is proposed in, for example, Published Unexamined Japanese Patent Application Nos. 3-93058 and 3-93056, which method utilizes a temperature increase within a light spot during reproduction to reconstruct information corresponding to such temperature increase part, or to reproduce information of those portions other than the temperature increased part in the spot.
In this case, certain light of substantially constant intensity was continuously irradiated as the reproduction light. Alternatively, as disclosed in JP-A-56-37834, pulsed light was irradiated at extra high frequencies. With such an arrangement, however, the pulsed light irradiation is effectively equivalent to continuous light irradiation because of the fact that the repeat frequency of such pulses is as high as several hundreds of megahertz or greater so that both the temperature on the recording medium and a reproduction output obtainable from reflection light are hardly responsive to a reproduction output of the pulsed light.
The prescribed prior art is encountered with a problem of inability to reproduce or play back any high-density record information because of a decrease in effective reproduction signal quality due to the fact that only part of the information of a light spot contributes to reproduction during playback of high-density record signals, thereby reducing the resultant reproduction signal output.
It is therefore an object of the present invention to provide a technique capable of avoiding the problem and of reproducing high-density recorded fine record marks at excellently high output with enhanced quality.
To attain the foregoing object the present invention employs specific means as will be set forth below.
When an optical recording medium is irradiated with light for reproduction of information on the optical recording medium by use of reflection light of the light, light is irradiated intermittently or alternatively in the form of pulses to detect reflection rays at at least two time points during irradiation of such intermittent light, thus obtaining a reproduction signal through mutual processing of resultant detection signals.
Whereby, it becomes possible to detect only a change in reflection light during irradiation of the reflection light, which in turn makes it possible to obtain a high signal output while enabling suppression of those portions other than such change component, thus obtaining a reproduction signal of excellent quality.
Additionally, it is also preferable that reproduction is done while causing the optical recording medium to reversibly change or vary in optical nature by irradiation of intermittent light.
It is thus possible to read, as a signal, only a change component of reflected detection light only at specific part whereat the optical nature was altered due to irradiation of intermittent light, which in turn leads to achievement of reproducibility with increased resolution.
Preferably, the reversible change in optical nature of the optical recording medium makes use of those caused by a change in temperature of the optical recording medium due to the intermittent light.
With such an arrangement, a significant change of reflected detection light is obtainable before and after irradiation of the intermittent light, thus obtaining an increased signal output.
It is also preferable that a series of intermittent light rays may be comprised of at least two light pulses.
The stability of reproduction light is thus improved obtaining good reproduction signal quality.
The invention provides a device at least having light irradiation means for irradiating light to an optical recording medium, and photodetection means for detecting reflection light of the light, and further having optical modulation means for recurrently irradiating light intermittently, first synch extraction means for extracting an output from the photodetection means in a way synchronized with the intermittent light, and second synch extraction means for extracting an output from the photodetection means at a time point different by a fixed time duration from that of the first synch detection means, wherein processor means is provided for performing operational processing of the outputs of the first synch detection means and the second synch detection means.
An extraction time difference between the first synch detection means and the second synch detection means may be shorter than a time period of irradiation of the intermittent light.
With these arrangements, it becomes possible to detect only a change component of the reflection light during irradiation of the same intermittent light, thus obtaining a high signal output while enabling suppression Of those other than such change component, which leads to an ability to obtain a reproduction signal of excellent quality.
In an optical record/reproduction device at least having light irradiation means for irradiating light to an optical recording medium, and photodetection means for detecting reflection light of the light, the device is arranged to at least have optical modulation means for recurrently irradiating light intermittently, delay means for causing an output from the photodetection means to delay for a predetermined time period, processor means for processing the output delayed by the delay means and the output from the photodetection means, and synch extraction means for extracting an output from the processor means in a way synchronized to the intermittent light.
The delay time of the delay means may be less than an irradiation time period of the intermittent light.
With these arrangements, it is possible to detect only a change component of the reflection light during irradiation of the intermittent light, thereby obtaining a high signal output while enabling suppression of those other than such change component; thus, a reproduction signal of excellent quality may be obtained.
Further, the intermittent light irradiation time may be shorter than the irradiation interval of the intermittent light.
This makes it possible to establish an appropriate cooling time of the recording medium to thereby ensure that a temperature change occurs stably, thus reliably obtaining the intended signal.
It is desirable that the intermittent light irradiation time, Tp, satisfies the relation which follows:
2 nanoseconds less than Tp less than D/v/4,
where D is the size of a light spot as formed on the recording medium during reproduction, and v is the velocity or speed of the light spot relative to the optical recording medium.
By letting Tp greater than 2 nanoseconds, it becomes possible to reliably provide a temperature rise of the recording medium, thus rendering the signal stably obtainable. In addition, by setting the irradiation time at a time taken for the spot to move a distance less than or equal to xc2xc of the spot diameter, those components of the reflection light other than the signal components become substantially identical at the instants before and after irradiation of light pulses, thereby making it possible to effectively suppress any unnecessary components.
A differential circuit is usable as the processor means. This makes it possible to extract a signal component alone with unnecessary components suppressed, thus obtaining excellent reproduction signal quality.
An operation of the present invention will be explained with reference to FIG. 5.
FIG. 5(c) shows an example of intermittent light 501 to be irradiated in the present invention. Due to the thermal action of the irradiation light, a temperature distribution 502 on an optical recording medium varies as shown in FIG. 5(b). Here, the medium used herein may be the one as taught by JP-A-3-93056 for example, which changes in optical nature at or above a certain temperature (referred to as xe2x80x9cmask formation temperaturexe2x80x9d) and renders effectively xe2x80x9cinvisiblexe2x80x9d (or masks) the information recorded on the medium (recording magnetic domains).
FIG. 5(a) is a diagram for comparing the visibility of the information on the recording medium at a time point immediately after light irradiation with that at an instant immediately prior to completion of the light irradiation. In the state 92 just before completion of the light irradiation, a significant change is observable at the center of a light spot between the light irradiation startup just-after state 91 and the light irradiation end just-before state 92. This is because a mask is formed at the light spot center due to an increase in temperature. Then, by processing the reproduction signals resulting from these two states, it is possible to detect only a change component of such two states. Here, one example was shown wherein differential processing is done by a differential detector 503.
At this time, since the light spot is slightly moved between the state 91 and the state 92, a change might also be observable in a signal from low temperature part; however, as far as such movement remains less than or equal to xc2xc the light spot diameter, such is not optically dividable so that any signal change at low temperature part may be negligible in practical use.